1. Field of the Invention
The present invention relates to an improvement of a manufacturing method for a glass film.
2. Description of Related Art
As is well known, flat panel displays (FPDs) have become mainstream as image display devices in recent years, the FPDs being typified by a liquid crystal display (LCD), a plasma display (PDP), an OLED display (OLED), and the like. Progress is being made toward further reducing the weight of those FPDs, and hence there is promoted further thinning of glass sheets used as a main component for the FPDs.
Further, for example, there is a growing use of an organic light-emitting diode not only for applications to a display that uses TFTs to blink light of three primary colors, but also as a plane light source, such as a backlight of the LCD and a light source for interior illumination, which emits only monochrome light. An illumination device that uses the organic light-emitting diode as a light source may have a freely deformable light-emitting surface as long as the organic light-emitting diode is constructed of a flexible glass sheet. Therefore, from the viewpoint of ensuring sufficient flexibility, there is also promoted further thinning of the glass sheet to be used for this type of illumination device.
As a method of cleaving the above-mentioned glass sheet to be used for the FPD, illumination device, and the like into a predetermined size, the following method is generally employed. That is, a scribe having a predetermined depth is engraved in the front surface or the back surface of the glass sheet along a preset cleaving line, and then a bending stress is applied to the scribe to cleave the glass sheet. However, in a case where the glass sheet is thinned into a state of a glass film, the scribe engraving itself is extremely difficult, and further, there may arise such a problem that the strength of the glass sheet significantly decreases due to a small defect such as a lateral crack formed in the cleaved surface. In particular, a long (band-like) glass film formed from molten glass by various manufacturing methods is required to be successively cleaved along the preset cleaving line extending in a delivery direction (longitudinal direction) of the glass film while being delivered in the longitudinal direction. However, the successive bending stress is not easily applied with high accuracy to the band-like glass film that is being delivered in the longitudinal direction thereof.
Therefore, when the band-like glass film is successively cleaved along the preset cleaving line extending in the longitudinal direction thereof, a cleaving method using a thermal stress has been employed in place of the cleaving method using the bending stress. Specifically, in this method, as described in Patent Literature 1 below, the band-like glass film is locally heated along the preset cleaving line extending in the longitudinal direction thereof while being delivered in the longitudinal direction, and then the locally heated portion (region) is cooled. As a result, a thermal stress is generated, to thereby successively cleave the glass film (in the longitudinal direction thereof).
In a case where the above-mentioned successive cleaving is performed in order to divide the band-like glass film into a portion to be finished into a predetermined glass product (hereinafter, referred to as “product glass portion”) and an unnecessary portion which cannot serve as a glass product (hereinafter, referred to as “unnecessary glass portion”), the product glass portion thus divided is continuously delivered to the downstream side and finished into a glass roll, a glass sheet having a predetermined dimension, or the like. On the other hand, the unnecessary glass portion thus divided is continuously delivered to the downstream side and sequentially broken into short glass sheets to be collected. Note that, the collected short glass sheets may be discarded directly, but are generally reused as a material for forming a glass film or the like.